Scottish power prepayment meter

Celster

I am having massive issues with Scottish power for my gas. I have had a prepayment meter with them for 8 years or so. There has NEVER been a time when I have topped up my meter that it hasn't taken a large percentage of that top up for debt!? I recently tried to leave Scottish power and go with OVO which acottish power refused twice to let me leave so I missed both installation dates for my new smart meter with Ovo and I assume it had been cancelled. To then receive a statment of estimated bills for the past year from Scottish power. The statments fluctuate between £178 in credit to £60 in debit. I understand that during the summer months I don't regularly top up my meter and I have a standing weekly charge. But even at the points where it is saying I am £178 in credit I am still being charge for debt when I top up. I spoke to an advisor for nearly an hour who really didn't grasp the situation and was telling me that my meter was actually in credit at the moment but it would probably be zeroed off as I was no longer a customer. I am now receiving emails, letters and phone calls telling me to pay £54 immediately. How they think i owe them £54 based on an estimate reading on gas I pay for before I use is beyond me. They now state they cannot read my meter as I am no longer with them? Please help im lost as to what to do next?